Patent GB-1415021-A (GB)
Title: Communication line multiplexing apparatus
IPC: H04L69/14
Filed: 1973-03-12
Abstract: 1415021 Data processing HONEYWELL INFORMATION SYSTEMS Inc 12 March 1973 [13 March 1972] 11851/73 Heading G4A A data processing system for serially receiving data from and transmitting data to a plurality of remote stations over a plurality of communication lines includes (1) an input/output controller comprising a memory 20 (Fig. 1B) having segments assigned to data to be received and data to be transmitted, each segment having a location for each communication line, (2) a central processor 9 (Fig. 1A) and (3) a memory 14 also having a location for each communication line, the system operating in three modes for transfer of data (a) an input/output mode in which the communication lines are coupled to the memory 20, (b) a scan mode in which the memories 14, 20 are coupled and (c) in a CPU mode in which the memory 14 is coupled to the processor 9. CPU mode.-An address from processor 9 causes read out to register 18 of a control word from memory 14. A counter 40 is checked to determine whether a full character is ready for transfer to the CPU and a counter 42 is checked to determine whether a character should be transmitted from the CPU. If transfer is not to be effected the control word is restored in memory 14. If transfer is to take place the data input transfer is first made, the character being fed to register 13 to wait until the CPU is ready, the data output transfer being similarly effected using register 13. Scan mode.-An address from processor 9 again causes read out to register 18 of a control word from memory 14. Simultaneously input/ output memory 20 is addressed to transfer 8 bits in the received segment, 8 bits in the transmit segment and 8 bits in a ready segment to registers 26, 28, 30 (each of the 8 bits relating to a different communication line). During a receive operation if the ready bit for the line being scanned is set, ready bit selector 32 increments receive sample counter 36 and transmit sample counter 38 in register 18. A count of 3 in counter 36 indicates the centre of the received bit and increments counter 40, the bit then being written into memory 14. During a transmit operation transmit selector 29 is enabled to send one bit from memory 14 via logic 16 to register 28 at a location determined by decoder 31. Subsequently, when the contents of register 18 are restored in memory 14, the contents of register 25 are stored in memory 20. Input/output mode.-128 communication lines L1-L128, Fig. 5 (not shown) are serviced in groups of four by line modules (LM1-LM32) which are enabled by a decoder (122) and a signal dependent on the transmission rate of the associated communication line. A baud rate interrupt BR1 may be generated at the end of either the scan or CPU modes to enable counter 99 which increments register 72 16 times so that the 120 bits of each of the segments of memory 20 are serviced. At each count of counter 99 the bits from memory 20 are loaded into register 28 and the enabled line module transmits received bits to register 26 and ready bits to register 30. The input/output mode may be in operation whilst the CPU and the memory 14 transfer data.